Breast hibernoma in a male patient: a rare case report and review of the literature

Abstract Hibernomas are uncommon, benign, lipomatous tumours of brown fat. Although hibernomas may arise from any region where brown fat exists, common locations include thigh, shoulder, back and neck. We report a rare finding of a breast hibernoma in a 43-year-old male. The patient was managed surgically with an excision of the breast mass. This report will outline the pathology and clinical findings of breast hibernomas and review of the literature.


INTRODUCTION
Hibernomas are uncommon, benign, lipomatous tumours of brown fat [1]. Brown fat is mainly present during foetal life and replaced by white adipose tissue; however, remnants of brown fat can persist into adult life [2]. The peak incidence of hibernomas is reported to occur within the third decade of life [3]. They commonly occur in areas of the thigh, shoulder and back. In this case report, we present the first male presentation of a hibernoma in mammary tissue and a review of the literature.

CASE REPORT
A 43-year-old male was referred by his General Practitioner to a breast surgeon with a large, right upper chest lump extending to his axilla. The lump had been present for almost a decade. Over the last several months, he had noticed it growing in size and discomfort with shoulder movement. He had no significant past medical history or family history of breast cancer or lipomas. He was a non-smoker and drinker with no regular medications. Clinically, there was a right-sided, upper-outer-quadrant breast mass, transitioning from firm to soft as it extended into the axilla. A small lump was also palpable at the 7 o'clock region without tenderness. The left breast demonstrated no tenderness or lumps, and no axillary or supraclavicular lymphadenopathy. The right nipple-areola-complex (NAC) was grade 3 ptosis and the left was grade 2, with bilateral soft gynecomastia present (Fig. 1).
He underwent an ultrasound, which revealed a large palpable lesion in the anterior right chest wall, measuring 16.3 × 5.4 × 16.1 cm, with a hyperechoic encapsulated lesion. The lesion contained a hypoechoic central focus measuring 2.1 cm without internal vascularity. At the 7 o'clock position, 6 cm from the nipple, there was a 26 × 17 mm hyperechoic avascular focus. He further underwent a breast magnetic resonance imaging (MRI), which demonstrated a circumscribed lesion of fat composition (68 × 130 × 140 mm) with mild internal vascularity, but no focal restricted diffusion or associated mass component. The lesion abutted the anterior margin of pectoralis major muscle and was away from the major neurovascular bundle. The patient underwent core biopsy of lesion, which confirmed the diagnosis of a hibernoma.
After extensive discussion, he underwent excision of right breast mass. Intra-operative findings included a large, partially encapsulated mass measuring 20 × 16 × 12 cm and weighing 865 g (Fig. 2). The mass was adherent to the pectoral fascia, but not infiltrating it and extending over lateral chest wall and axilla with extensive neovascularisation around the mass. Histopathological assessment showed a lobulated, fatty lesion with many of the adipocytes demonstrating features of brown fat and no evidence of malignancy. The patient recovered well post-operatively and was reviewed one month post-operatively with no complications.
The largest series published to date about hibernomas (Soft Tissue Registry of the Armed Forces Institute of Pathology) reported 170 cases, of which 99 were men and 71 being women. The mean age of tumour development was 38.0 years ranging from 2 to 75 years [1]. Common anatomic locations included thigh, shoulder, back, neck, chest, arm, abdominal cavity, and retroperitoneum, accounting for only 1.6% of benign lipomatous neoplasms [6]. Breast hibernomas are relatively uncommon and almost all cases are reported in females. Clinically, majority of cases present as a slow-growing, asymptomatic mass, which can cause symptoms due to compression of adjacent structures or diagnosed as an incidental finding at a radiological routine examination [8].
A search of the literature was conducted using the terms 'hibernoma' and 'breast' or 'mammary' across multiple databases including Embase, Pubmed and Google Scholar. Relevant criteria included that the article was not a review article, included a diagnosis of hibernoma and was localized either to the breast or mammary tissue. Of the 495 articles identified, nine articles satisfied the criteria with an average age 45.5 years (range: 29-69). The most common presentation was a painless mass, occurring in five cases. Two cases reported pain, and the remainder two were incidental findings on routine imaging. The majority of cases were managed with surgical removal of the mass (7/9), with two patients opting for regular follow-up and reassurance. There were no cases of malignancy or neoplastic changes ( Table 1).
The most common workup for breast masses follows the triple assessment with ultrasound, mammography and biopsy. Hibernomas on ultrasound present as hyperechoic, well-circumscribed ovular masses with uniform echogenicity [9], whereas angiography shows highly vascularized tumours with occasional arteriovenous shunts [10]. On MRI, lesions demonstrate signal intensity like subcutaneous fat on both T 1 and T 2 weighted images, with  were clean and patient is disease free at 23 months follow-up contrast enhancement due to hypervascularization [11]. However, no specific imaging features exist to distinguish hibernomas from other benign or malignant soft-tissue tumours [12], such as lipoma, angiolipoma, malignant fibrous histiocytoma and liposarcoma [13]. The present case was managed with complete surgical excision, as is the common practice for hibernomas. The Soft Tissue Registry of the Armed Forces Institute of Pathology series revealed no recurrence or aggressive behaviour [1]. As hibernomas do not have malignant potential, there is currently no role of neoadjuvant or adjuvant chemotherapy or hormonal therapy. The management should be in line with other benign masses of the breast aligned with principles of breast lumpectomy and reconstruction.

CONCLUSION
Hibernomas are benign tumours closely related to brown adipose tissue, which is normally present and active in humans from foetal life through adult life. A comprehensive history and triple assessment is the cornerstone to workup and management of these relatively benign masses.